Sonar apparatus, particularly for deep-sea fishing

ABSTRACT

A sonar system, particularly for use for deep-sea fishing, which produces an indication, either optical or acoustical, representative of the received signals which shows not only the range of the reflecting object but additionally whether the reflecting object is a single object or a plurality of closely bunched objects. The transmitted signals are relatively long keyed pulses each of which contains a plurality of nonmonochromatic oscillations which have a distinct predetermined arrangement in time, and has a broad bandwidth as compared to the center frequency of the oscillations. A voltage proportional to the instantaneous or momentary frequency of the received signals is then utilized to modulate the ranging or distance proportional voltage in the indicating device, e.g. a cathode ray tube of an echograph, in order to produce the additional indication representative of the type of reflecting object.

0 United States Patent 1 3,696,328

Schwartz 1 Oct. 3, 1972 [541 SONAR APPARATUS, PARTICULARLY FOR DEEP-SEAFISHING Primary Examiner-Richard A. Farley [72] Inventor: WernerSchwartz, Bremen- Attorney-Spencer & Kaye Oberneuland, Germany [5 ABS CT[73] Assignee: Fried Krupp Gesellschaft mit beschraenkter, H ft Essen,Gen sonar system, particularly for use for deep-sea fishmany mg, whichproduces an indication, either optical or acoustical, representative ofthe received signals [22] Filed May 1970 which shows not only the rangeof the reflecting ob- [21] Appl. No.: 39,315 ject but additionallywhether the reflecting object is a single object or a plurality ofclosely bunched objects. The transmitted signals are relatively longkeyed pul- [301 Forelgn Application Pnonty Data ses each of whichcontains a plurality of nony 1969 Germany 19 27 172-3 monochromaticoscillations which have a distinct predetermined arrangement in time,and has a broad U.S. R, R, as compared to the center frequency of theIII!- oscinations A voltage proportional to the instantane. [58] Fieldof Search ..340/ 3 FM, 3 D, 3 R; ous or momentary frequency of thereceived signals is 343/172 R then utilized to modulate the ranging ordistance proportional voltage in the indicating device, e.g. a {56]References C'ted cathode ray tube of an echograph, in order to produceUNITED STATES PATENTS thel addition?! indication representative of thetype of re ec n o ec 3,332,056 7/1967 Drenkelfort ..340/3 R g 13,487,409 12/ 1969 Thiele et al. ..343/ 17.2 R 14 Claims, 16 DrawingFigures DiITerenI/a- (or PAIENTEUum I972 3.696.328

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SONAR APPARATUS, PARTICULARLY FOR DEEP- SEA FISHING BACKGROUND OF THEINVENTION The present invention relates to a sonar apparatus,particularly for use in deep-sea fishing, with a transmitting device forthe directed emission of keyed transmitted pulses each having aplurality of non-monochromatic oscillations, and with a receivingarrangement connected to a receiving base provided with means forconverting the received signals in order to provide a preferably opticalor acoustical representation of the ranging information.

Known radar system of this general type provide satisfactoryrepresentations for dot-shaped and for linear objects, for example, byclear indication on the screen of a cathode-ray tube. In one suchconventional system the image point or points become brighter on theface of the cathode-ray tube depending on the objects in the sectorbeing covered by the radar device, after radial deflection of thecathode beam of the cathode-ray tube by an output voltage from a timediscriminator which is proportional to the distance of the reflectingobject. When cathode-ray tubes are used, this time discriminator isusually an integrator controlled by a constant voltage or anothersawtooth generator. When writing indicators, the so-called echographs,are used to present the ranging information, the time discriminator isthe writing stylus which moves at a constant speed.

The result of the ranging information indication according to this orany other known processes, which will be discussed later, isunsatisfactory, however, in the case of an areal or voluminouscongregation of individual objects, e.g., a school of fish, as occursparticularly in deep-sea fishing. This is due to the fact that in thesecases of areal or voluminous congregations of individual objects,theranging information is represented, for example, on the screen of acathode-ray tube, as in the case of a single reflecting object only inthe form of a line or dot, respectively, corresponding with the centerof mass of the entirety of the covered, closely bunched objects. Thefisherman, however, is very interested in being able to determine, fromthe ranging information offered on the screen of the cathode-ray tube oron the paper strip of the echograph, whether this information originatesfrom individual large rocks, wrecks, large-size individual fish or otherindividual dot-shaped reflecting objects or whether this is an entireschool of fish which would promise a worthwhile catch and should beapproached.

It would therefore be highly advantageous if a system of the generaltype mentioned above could be provided which permits unequivocalconclusions from the ranging information obtained and indicated e.g. onthe screen of a cathode-ray tube, as to whether the representationoriginates from an individual dotshaped object or from a larger numberof bunched individual objects. The present invention which supplies thisneed is based on the following observations and contemplations: A schoolof flsh consists of a large number of dot-shaped reflecting objectswhose position with respect to one another is continuously changing. Aslong as during the ranging process the duration of the transmittedpulses is short when compared to the travel time difference between theindividual echoes of individual fish from the school of fish, separateechoes result which lead to separate dot-shaped representations in theillustration of the ranging information on the screen of the cathode-raytube. While it is known that the shorter the transmitted pulse, thebetter the distance resolution, i.e. the better the individual echoeswill result in separately illustrated dot-shaped representations withoutany mutual time influence, it is also known that very short transmittedpulses, due to their being relatively broadbanded, require a substantialamount of apparatus for accomplishing the echo sounding and moreoverhave the drawback that their echoes can not very easily be recognizedand represented due to the high noise level. While it is possible toachieve a more favorable signal to noise ratio by utilizing transmittedpulses of longer duration, the representation of the information is thenpredominantly composed of time overlaps of the individual echoes. Theknown use of keyed sine wave pulses as the transmitted pulses in suchapplications leads to falsified representations of the ranginginformation because the received signals all consist only of frequencycomponents of the same fundamental frequency, i.e. the transmittingfrequency. This then results,in the known systems, in theabove-mentioned representation of predominantly the center of mass ofthe school of fish as a luminous point on the screen of the cathode-raytube without any indication of the fact that the reflections are notfrom an individual reflecting object being recognizable on the screen ofthe cathode-ray tube.

High-quality sonar systems contain devices for the combinedrepresentation of the sounding information to indicate not onlythedistance of the reflecting objects but also their lateral deviation fromthe main direction of the major lobe of the sending/receivingcharacteristic. With such a system, for example, as disclosed in GermanPat. No. 977,599, monochromatic or quasimonochromatic transmitted pulseswhose duration is adapted to the requirements for distance resolutionand for the signal to noise ratio are used. In this system, theinformation with respect to the lateral deviation is derived from thephase difference between the signals received by means of two receiversor two groups of receivers. However,.almost no information is providedwith respect to the extent of a located aggregation of individualobjects transverse to the propagation direction of the transmittedpulses. The components of the received signals or voltages originatingfrom the individual dot-shaped reflectors in the form of individualfish, as well as the oscillations of the transmitted pulses, aresinusoidal and contain as their fundamental the carrier frequency of thetransmitted pulse. A travel time discriminator with a subsequentlyconnected delay member or subsequently connected integrator with a timeconstant which is large compared with the period of the carrierfrequency is connected to the two receivers or groups of receivers andthus furnishes an output voltage corresponding to the average phaseposition of all of the individual reflectors for the transversedeflection of the electron beam in the cathode-ray tube. That is, thesounding or ranging information represented again correspondssubstantially to the type of information which would result from asingle reflector at the center of mass of the school. The informationthat this is in fact an entire school of fish is again lost.

It is known for different fields of application to provide radar systemswith transmitted pulses comprising a mixture of a plurality offrequencies instead of using monochromatic transmitted pulses. Thecorrelation process disclosed for the first time in Swiss Pat. No.220,877 employs a mixture of different frequencies, preferably even anoise signal, for the unequivocal distance measuring of individualobjects in spite of the presence of substantial interference components.Moreover, the use of two different frequencies for sonar is known, forexample, as disclosed in German Pat. No. 1,017,054 for the distinctindication of the interfare between mud and solid bottom in bodies ofwater. Other known apparatus employ sonar devices with linear ornonlinear frequency-modulated oscillations to produce a continuousrepresentation of the sounding information which is no longer dependenton the periods given by the transmission of keyed pulses.

None of these or any other known device, however, is based on theproblem of the present invention, nor do the teachings disclosed thereinrepresent concrete indications as to how the problem can be solved byfurnishing sonar systems with a representation of the soundinginformation from objects according to their distance and if necessarydirection with simultaneous differentiation between individualdot-shaped objects and areal or voluminous congregations of individualobjects after conversion of the received voltages.

SUMMARY OF THE INVENTION The above-mentioned problem, of distinctlyindicating individual objects, as for example entire schools of fish,has been solved for sonar systems by the present invention in thattransmitted pulses of long duration are used which exhibit a distinctarrangement of the oscillations with respect to time and which arebroadbanded when compared with the characteristic center frequency ofthe oscillations, and an identifying voltage which is proportional tothe momentary or instantaneous frequency of the received signal isgenerated and utilized to modulate the ranging information in theindicating device.

The problem on which the present invention is based is solved by theabove-mentioned special selection and combination of the transmittedpulses and conversion of the received voltages for representing thesounding informations. This solution is based on the use of the knownfact that a dot-shaped reflector reflects the transmitted signal exactlyto the location of the receiving base so that the original order of thetransmitted pulses is again contained in the received signals. Incontradistinction thereto, the original time arrangement within thetransmitted pulses does not appear in the same order in the receivedsignals when components from different, particularly from independentlymoving, dot-shaped reflecting objects located at different distances,and thus having different travel times, are superimposed at thereceiving end.

The teaching according to the present invention therefore requires thepossibility for the displacement of the defined time arrangement of theoscillations originally contained in the transmitted pulse. Such adisplacement is used as a criterion for the presence of an aggregationof individual reflectors as additional information during the conversionof the received signals or voltages for the representation of theranging information. According to the present invention an identifyingvoltage is used for this purpose which is proportional to the momentaryor instantaneous frequency of the received voltages and which serves tomodulate the means for converting the received voltages into arepresentative indication. From the use of statistical methods in theradar art, it is known to impart a certain identification to thetransmitted signal, for example, a time pattern produced by digitalcoding. The received signal is then conducted through an optimum filterwhich furnishes an output voltage only in the case of a signal whichreturns without displacement. Such systems, however, are very expensiveand complicated in their apparatus so that while they can be used forspecial applications, they will never gain acceptance in the commercialfishery industry. Moreover, such installations do not always give adistinguishable evaluation of individual dot-shaped reflecting objectsas compared to a congregation of dot-shaped objects, since this type ofproblem has thus far not been acute in such systems.

In contradistinction thereto, the solution of the problem provided bythe present invention represents a device which can be realized withrelatively simple circuit means since the determination of the momentaryfrequency of the received voltages as well as the use of an identifyingvoltage proportional to these momentary frequencies for the modulationof the signal conversion means for the received voltages to provide arepresentation of the sounding information does not produce anydifficulties as regards circuitry. It is only necessary for this purposeto use transmitted pulses of the abovedescribed type, i.e. pulses whoseoscillations have a wide bandwidth with simultaneously only a slightfluctuation of their momentary frequency during the duration of thepulse. With the additionally selected long duration of the transmittedpulses there is thus provided the possibility for a noticeabledisplacement of the original order or arrangement of the oscillationswithin each transmitted pulse as the criterion for the presence of acongregation of individual reflecting objects with a simultaneouslyfavorable signal to noise ratio.

It is possible, for example, to frequency-modulate the oscillations of atransmitted pulse during the duration of this pulse, linearly with time.The received voltages originating from a single reflecting object wouldthen also exhibit this rise in the frequency of the oscillations and theidentifying voltage proportional to the momentary frequency could thenhave a continuously rising course. If the transmitted pulses werereflected from a congregation of individual dot-shaped objects, themomentary frequency of the received voltages would not exhibit thiscontinuously rising course, but would fluctuate strongly and so wouldthe course of the identifying voltage. Because of the simple evaluationpossibility for the modulating identifying voltage, a linear frequencymodulation of the transmitted pulses would be preferable, althoughprincipally the same characteristic result also could be achieved withother time sequences for the momentary frequency of the transmittedpulse oscillations.

However, frequency modulation has the drawback that the requirements fora momentary frequency which is as constant as possible over time and atthe same time for a wide bandwidth for the oscillations of thetransmitted pulses, i.e. the requirement for an identifying voltagewhich is as constant as possible for dot-shaped individual objects andconversely is strongly fluctuating for a congregation of objects,contradict one another. It is therefore more advantageous, according toanother embodiment of the present invention, to utilize, transmittedpulses having oscillations of unchanging frequency which arephase-adjusted according to a predetermined code. Whereas in this casethe momentary frequency of the individual oscillations is constantexcept for the moment of the phase shift, the total spectrum of theseoscillations is very broad due to the phase adjustment. A suitable codefor this purpose is the so-called Barker code which had originally beendeveloped for other purposes. Other codes which are less commonly useddue to their characteristics with respect to their autocorrelationfunctions being inferior to those of the Barker code, can also be usedfor this purpose but can not be grouped under a typical name. If acertain fluctuation of the identifying voltage between two limit valuesis disregarded, this will result in an advantageous further widening ofthe effective spectrum of the oscillations of each transmitted pulsewith the use of a coded shift adjustment between oscillations of atleast two different frequencies.

In order to be able to determine fluctuations in the identifying voltagewhen the original order of the oscillations are disturbed, it isadvisable to determine the number of zero voltage crossing of theoscillations in the received voltage during a predetermined observationtime period which is short when compared with the duration of thetransmitted pulses. Advantageously this observation period is selectedin the order of magnitude of the period of the center frequency of theoscillations.

A useful possibility for representing the sounding or ranginginformation is the optical representation on the screen of a cathode-raytube after converting the received voltages by means of the alreadymentioned time-proportional deflection of the cathode beam which isbrightness-controlled by the arrival of the received voltages. While themodulation by the identifying voltage can be accomplished by brightnessmodulation of the beam, a transverse deflection of the beam according tothe time pattern of the identifying voltage is more appropriate. Thiswill then no longer produce a single luminous spot, but rather a blurredarea of somewhat reduced brightness. This modulation can also beexpanded in such a manner that. whenever the identifying voltage exceedsa certain waviness, i.e., at the presence of the criterion for acongregation of individual objects, an oscillator, for example, anastable multivibrator, is turned on to produce a uniform blurred area onthe face of the cathode-ray tube by means of a uniform transversedeflection of the cathode beam which is brightness-controlled by thearrival of the received signals.

According to another feature of the invention, in place of thecathode-ray tube, another commonly used device for the opticalrepresentation of the sounding information, i.e., an echograph, may beutilized. In such a device the stylus used as the means for convertingthe information does not normally provide for the possibility of adeflection transverse to its direction of travel. While the modulationcould be accomplished by blackening the graph, according to the presentinvention, a vibrating transverse deflection of the moving stylus isprovided by electromechanical means so that there is again produced anareal representation in the case of an aggregation of individuallyreflecting obects.

According to another feature of the invention, particularly for use indeep-sea fishing, an acoustical representation of the ranginginformation may be provided either instead of or in addition to theoptical representation. If such an acoustical representation isprovided, then it is advisable to modulate the amplitude or, moreeffectively, the frequency, or both, of the acoustic representation ofthe received signal with the identifying voltage after converting thereceived signals to an audible frequency range if necessary.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 shows the principal circuitdiagram of a sonar system supplemented by one embodiment device of thepresent invention comprising a receiving arrangement with means for theadditional conversion of received voltages for the purpose in thisembodiment of optically representing the sounding information on thescreen of a cathode-ray tube in order to provide indications having adifferent characteristic for a dot-shaped object and for a wholecollection of reflecting objects.

FIG. 2a shows a time-proportional frequency modulated transmittedsignal, here a rectangular wave, plotted over time.

FIG. 2b shows the course of its momentary frequency, or the identifyingvoltage proportional thereto, plotted over time.

FIG. 3a illustrates an example of a received signal, plotted over time,resulting from a reflection from a voluminous collection of individualobjects for a transmitted pulse according to FIG. 2a.

FIG. 3b shows an example for the resulting momentary frequency, or theidentifying voltage proportional thereto, respectively, in their coursesover time for the received signal of FIG. 3a.

FIG. 4a shows the l3-digit Barker code.

FIG. 4b shows the course of sinusoidal oscillations of constantfrequency which where phase-shifted by according to the Barker code.

FIG. 40 shows the course of the momentary frequency over time for thesignal of FIG. 4b.

FIG. 4d shows the spectrum of the frequency according to FIG. 4b overthe frequency axis.

FIG. 4e shows a principal block diagram for producing the course shownin FIG. 4b.

FIG. 5a shows the course of two sinusoidal oscillations which areshifted according to the code of FIG. 4a to alternate between twodifferent frequencies.

FIG. 5b shows a principal block diagram for producing the course shownin FIG. 5a.

FIG. 6 is a schematic illustration of a writing device whose recordingcan be modulated by the identifying voltage according to the invention.

FIG. 7 is a principal block diagram illustrating the modulation of anacoustical representation of the sounding information by means of theidentifying voltage according to another embodiment of the invention.

FIG. 8 illustrates the use of the present invention with a sonar systemhaving a base consisting of two resonators or two groups of resonatorsand producing an indication of the ranging information on the screen ofthe cathode-ray tube.

FIG. 9 illustrates a modification of the embodiment of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, thereis shown a block diagram of a ranging device 1 which produces atransmitted signal 2 consisting of keyed pulses having, in this example,linearly frequency-modulated oscillations 4. The signal generator 5,which operates with a center frequency of for example f 30 kHz,furnishes the oscillations 4 to a modulator 6 where they arefrequency-modulated to produce the signal 4a. The output of modulator 6is fed to a keying circuit 7, controlled by a pulse generator 8 whichforms the transmitted pulses 3 of a certain duration D from the thusmodulated wave train 4a of the oscillations 4. The output pulses fromthe pulse generator 8 are simultaneously utilized to accomplishsynchronization to the initial frequency of modulator 6. The signal 2which is to be transmitted is fed to a base 11, which in this circuitdiagram contains a single resonator 12, via a transmitter amplifier 9and a duplexer l commonly used in sonar devices, particularly in theecho sounding art. The double arrow 13 indicates that this base 1 1 maybe pivotal. The possibility of pivoting only the transmitting/receivingcharacteristic 14 with the characteristic aperture angle a by electricalmeans instead of the entire base 11 will be discussed later inconnection with FIG. 8.

In order to illustrate the various types of indications which willresult with the system according to the invention, let it be assumedthat at first there is only a single dot-shaped object 16 in front ofthe base 11, for example exactly on the main axis of thetransmitting/receiving characteristic 14, and that moreover, a portionof a larger collection of individual objects, hereinafter called aschool of fish 17, is being sounded. The physical conditions in sonarare known, see e.g. D.G. Tucker Sonar in Fisheries London 1967, Chaptersl and 2.

The processing of the returning echo, i.e. the conversion of receivedvoltages for the representation of the sounding information, isinitially also well known in the state of the art and is thusillustrated only in principle in FIG. 1 and in the followingdescription. In order to represent the ranging information, the outputsignal from a monostable multivibrator 18, which is placed in its labileswitching state at the beginning of each transmitted pulse 3 by theoutput pulse from pulse generator 8, controls the deflection, e.g. thevertical deflection, of an electron beam of a cathode-ray tube 20 via anintegrator 19, and thus effects a distance-proportional deflection ofthe luminous dot 30 from the zero marker 21 of the screen 22. On thisscreen 22, however, an indication in the form of a luminous dot 30appears only when, due to arriving echoes, the Wehnelt cylinder 23 ofthe cathode-ray tube 20 is brightness-controlled by the, voltage 14corresponding to the received signal, generally via a receiver amplifier24. In the illustrated example, the integrator 19 is reset, and thus theelectron beam of the cathode-ray tube 20 is reset to the zero marker 21,when the monostable multivibrator l8 flips back to its stable switchingstate. Since it must be assured that this resetting occurs within theinterval between two conservative transmitted pulses 3, a control line25 is provided between the pulse generator 8 and a control input of themonostable multivibrator 18. Via the line 25 the transient time constantfor the duration of the labile switching state of the monostablemultivibrator 18 is also correspondingly changed whenever the pulsegenerator 8 switches to another repetition frequency for the transmittedpulses 3.

The above described receiving arrangement according to the state of theart for sonar systems is now supplemented according to the presentinvention by means for converting the received voltages u for therepresentation of the ranging information with the possibility providedfor differentiating individual dotshaped objects 16 from the indicationof a school of fish 17 on the screen 22 of the cathode-ray tube 20. Forthis purpose, the instantaneous or momentary frequency f of the receivedvoltages u is determined, for example, by counting the number of zerocrossings of the oscillations of the received voltages u during apredetermined observation period AT, and is converted into aproportional identifying voltage u by means of a digital-analogconverter 26. The measuring time for the observation period AT may bethe pulse width of an astable multivibrator 27 which is connected with agate input of the digital-analog converter 26. Such a converter 26, in asimple embodiment, may consist of an integrator which is charged instages during the observation period AT by input pulses, which, in theillustrated embodiment, are furnished by a Schmitt trigger 28 setapproximately to a trigger voltage of zero; and thus are generated whenthe momentary values of the voltages together with the oscillations ofthe received voltages 14,. change from the negative to the positive. Theobservation period AT is selected in the order of magnitude of theperiod of the characteristic center frequency f,,, of the modulated wavetrain 4a of the oscillations 4 in the transmitted pulses 3. Identifyingvoltages u is applied after adaptation in an amplifier 29 if required,to the deflection system of the cathode ray tube 20, and serves todeflect the electron beam in the cathode-ray tube 20 in a directiontransverse to the distance-proportional deflection caused by the voltagefrom integrator 19.

The individual dot-shaped object 16, in convential devices according tothe state of the art, would lead to a luminous dot 30 on the screen 22of the cathode-ray tube 20 during the representation of the ranginginformation. Since, however, in the selected example the transmittedpulses 3 contain a linearly modulated wave train 4a whose timearrangement is not substantially changed when reflected by a dot-shapedobject 16, the identifying voltage a is no longer constant but changesduring the duration D of each transmitted pulse 3 proportionately to thecourse of the momentary frequency f. If it is assumed that a momentaryfrequency f below the center frequency f,,, leads to a lateraldeflection of the cathode beam toward the left on the screen 22, thenthe indication resulting from the received voltage u on this screen 22of cathode-ray tube 20 is an inclined line 31 corresponding to theenlarged illustration in FIG. 1. With only a slight change in time ofthe momentary frequency f during the duration D of the transmittedpulses 3, the fluctuation in the identifying voltage 14,, is also onlyslight, so that, in practice, there is still produced for the observerthe impression of a luminous dot 30 due to the storage and overshooteffects of the screen 22 of a cathode-ray tube 20.

If, however, reflected portions of a statistic collection of individualdot-shaped objects, as they are assumed to be represented by the schoolof fish 17, are superimposed in the received voltage 14,, then theoriginal time arrangement of the oscillations 4 is no longer containedin the received voltages u Rather a large displacement of the timesequence of the zero crossings of the modulated wave train 40 within thereceived voltages u and thus a large fluctuation in time of theidentifying voltage u results due to the superimposition or overlappingof the various components and the influence of the different distancesfrom base 11 at which the individual fish are disposed, quite aside fromDoppler effects from the individually moving reflecting objects.Consequently, the electron beam now does not experience a continuoustransverse deflection corresponding to the inclined line 31, but ratherthe transverse deflection fluctuates strongly during the passage of thetransmitted pulse 3 through the section of the school of fish beingcovered. Due to the strong fluctuation of the electron beam there now appears an areal brightening 32 on the screen 22 which is clearlydistinguishable from the previously described dot 30 indicating a singlereflecting object 16. Due to the rapid lateral deflection of theelectron beam this area] brightening 32 is normally not as luminous asthe luminous dot 30.

This difference in brightness can be compensated with simple, additionalmeans or can be overcompensated if desired by applying the identifyingvoltage u,, to a second input of the receiving amplifier 24 toadditionally control the Wehnelt cylinder 23. To produce a particularlylarge lateral deflection of the electron beam, it is advisable toconnect a differentiating stage 33 ahead of amplifier 29 so that thegreater the displacement of the original order of the modulated wavetrain 4a, i.e., the greater the time fluctuations of identifyingvoltages u the greater will be the control voltage applied to amplifier29.

FIGS. 2a and 2b illustrate the relationship between the modulated wavetrain 4a, here a rectangular oscillation, within a transmitted pulse 3of the duration D, and the momentary or instantaneous frequency f, onebelow the other. The identifying voltage u proportional to the momentaryfrequency f passes through zero for the center frequency f,,, and haspositive values for the higher frequency of the modulated wave train 4a.Whereas in FIG. 2a the oscillations of the received voltages u have thesame time sequence as the modulated wave train 4a within the transmittedpulses 3 due to the presence of a dot-shaped reflecting object, FIGS. 30and 3b show the relationships for the same transmitted pulses 3 but withreflection from a school of fish 17. The original time sequence of theoscillations 4 of the received voltage u is now very much disrupted, andthe time sequence of the various momentary frequencies f is greatlydisarranged. The course of the identifying voltage 14,, (FIG. 3b) nowfluctuates correspondingly great, which leads to the describedirregular'transverse deflection of the electron beam and thus to theareal brightening 32 on the screen 22 of the cathode-ray tube 20 of FIG.1.

The above explanation of the origin of the areal brightening 32 ascompared with the luminous dot 30 on screen 22 of FIG. 2 indicates thatfor a distinct differentiation between these two indications atransmitted signal 2 should be selected which has a momentary frequencyf as constant as possible, but still exhibits a broad spectrum of theoscillations within the transmitted pulse 3. Such a signal can beproduced, even better than by the linear frequency modulationillustrated in FIG. 2a, by phase shifting a constant frequency signal fwhich is assumed to be a sinusoidal oscillation in FIG. 4b, in a knownmanner according to a suitable code. For demonstration purposes the 13-digit Barker code was selected to phase shift the oscillations by 180 asshown in FIG. 4a. FIG. 4c shows the substantially constant course of themomentary frequency f, because the differences between two zero passagesof the same orientation are constant with the exception of the points intime at which there occurs a phase shift. A reflection of such atransmitted pulse from a single dot-shaped object 16 thus leads to anonly slightly distorted luminous dot 30. Since, however, the actuallyresulting spectrum of a thus modulated wave train 4b of FIG. 4b, asshown in the sketched illustration of FIG. 4d, is very broad whencompared to frequency f of the individual oscillation, the reflection ofsuch a transmitted pulse from a school of fish 17 leads to a very strongdisplacement of the frequency arrangement with respect to time and thusto a clear areal brightening 32 on the screen 22 of the cathode-ray tube20 The principle circuit diagram shown in FIG. 4e shows an example forproducing this resulting wave train 4b. The frequency f, from thefrequency generator 5 is switched by a switch 51 either directly on thekeying circuit 7 or via a l-phase shift 51a, e.g. represented by anoperational amplifier, that as is well known inverts polarity of anoutput signal as compared with the input signal. The switching of switch51 is accomplished by a code generator 52.

A further possibility to provide a signal 2 which is suitable for theproblem at hand, is to shift the frequency between, e.g., two constantfrequencies f and f according to a code, for example the code shown inFIG. 4a. The resulting wave train 5a within a transmitted pulse ofduration D can be derived, for example, from the principal circuitdiagram shown in FIG. 5b. Here a switch 51 switches between twogenerators 5a and 5b for the constant frequencies f and f and the thusmodulated wave train 40 is given directly to the keying circuit 7 (seeFIG. 1). The switching of switch 51 is accomplished by a code generator52 which in a known manner produces, for example, the Barker code ofFIG. 4a through a feedback-connected shift register. Such a shifting ofthe oscillations between different frequencies need of course not belimited to two constant frequencies f, and f Thus far, only therepresentation of the sounding information on the screen 22 of acathode-ray tube 20 was discussed. However, the teaching of thisinvention can also be advantageously applied to ranging systems providedwith an echograph 34 (FIG. 6) since with such writing indicator devicesthe possibility of being able to distinguish between echoes fromindividual dotshaped objects 16 and those from, e.g. a school of fish 17represents a desirable increase in the available information. However,the utilization of the identifying voltage u is not as easy in this caseas with the cathode-ray tube 20, since the stylus 35 of an echograph 34which as illustrated is normally guided across the recording paper 36 ina straight line and at constant speed, would have to be provided with anadditional electromechanical device for a transverse deflection duringits longitudinal movement in order to be able to provide a marking inthe event of the arrival of a received voltage u This device wouldbecome effective in the case of a fluctuating identifying voltage u Theother possibility to express the additional information about the typeof the reflecting object is the degree of darkness of the written lines(indication 40) on the recording paper 36 by influencing the writingvoltage of stylus 35 with the identifying voltage u which is not verypracticable since the degree of darkness of an echogram fluctuatessubstantially in any case due to the multitudinous informations beingoffered. In FIG. 6 therefore the example of the solution of theelectromechanical transverse displacement of the stylus 35 is selectedwhere the stylus slides past a slide 37. This slide 37 is nowmechanically coupled with an electromagnet 38 by means of a leverarrangement 39 which causes the slide 37 to vibrate transverse to thedirection of movement of the stylus 35 whenever a fluctuatingidentifying voltage u excites this electromagnet 38 through the poweramplifier 29a. In the cases of the individual dot-shaped objects 16 andthe school of fish 17 shown in FIG. 1 this device then leads to theindication 40 which, for the purpose of a clearer illustration, is shownin FIG. 6 removed from the momentary path of stylus 35. It is of courseunderstood, that when the echograph 34 is used instead of cathode-raytube 20 a number of structural components from FIG. 1, i.e. integrator19 and pulse generator 8, can be eliminated since with the echograph,the continuously driven stylus 35 as indicated controls the modulator 6and keying circuit 7 of FIG. 1, and hence the transmitted signal 2, bymeans of a signal generated through a stylus contact 41.

The above-described examples relate to the differentiation between asingle reflecting object 16 and a voluminous aggregation of individualobjects, i.e., the school of fish 17. In a similar manner, the apparatusaccording to the present invention also permits a differentiationbetween linear and area] reflecting objects covered by radar systemswhich would all be indicated as a line on the screen of ranging systemsaccording to the state of the art.

A sole or additional acoustical representation of the soundinginformation is often employed particularly for deep-sea fishing. Such anacoustical indication represents a substantial aid to the fisherman,since he receives signals relating to changes in the sounding conditionseven when he does not happen to be on the bridge or observing theoptical instruments. A circuit diagram of such a system according to theinvention is shown in FIG. 7, where the received voltages u coming fromthe duplexer are given to a mixer stage 43, if necessary via apreamplifier 42. A signal generator 44 furnishes the frequency signalrequired to convert the input signal u into the audible range. At theoutput of mixer stage 43 a headset or loudspeaker 46 is connected, ifnecessary via a final amplifier 45. The identifying voltage u in theillustrated example is used both for amplitude modulation, byinfluencing the amplifiers of the final amplifier 45, and for frequencymodulation by detuning the signal generator 44. Obviously, how ever,either one of the modulation techniques could be used alone. With aconstant identifying voltage 14 i.e. with received voltages u in theranging system which originate from a single dot-shaped object 16, thefrequency and volume of the acoustically represented soundinginformation are approximately constant, whereas with a stronglyfluctuating identifying voltage u i.e. with received voltages uoriginating from a school of fish 17, the frequency and volume fluctuatenoticeably in the loudspeaker 46. Thus, it is easily possible todifferentiate from the acoustical impression, whether the soundinginformation originates from a single object 16 of no interest to thefisherman or whether the sounding system 1 has just located a school offish 17.

The sounding system arrangements la and lb shown in FIGS. 8 and 9 with asubdivision of the base 11 into two groups of resonators 12a, 12b arealso known per se. Their advantage when compared with the soundingsystem 1 shown in FIG. 1 is the possibility of pivoting thetransmitting/receiving characteristic 14 by electronic means or to beable to measure the angular deflection of a reflecting object from themain axis 15 of the transmitting/receiving characteristic 14. For thispurpose the two groups of resonators 12a and 12b, whose acoustic centersare disposed at distance d from one another, are controlled through adelay network 47 which is itself controllable by means of a phase setter48 to select the direction y of the main axis 15 with respect to theaxis 49 normal to the base 1 1.

As disclosed in German Pat. No. 966,599, the phase angle betweenreceived voltages a and i4 is determined by means of a phase detector50, e.g. a phase meter which is tuned approximately to the centerfrequency of the oscillations, and a voltage proportional to the phasedifference produced. The output signal from the phase meter 50 ismultiplied with the momentary value of the voltage for the distancedeflection from integrator 19 in a multiplier 51 and this productvoltage u now serves to deflect the electron beam transversly to thedirection of the distance-proportional deflection.

According to the present invention, this product voltage u issuperimposed with the identifying voltage u which was amplified inamplifier 29 if required, so that in the case of a fluctuatingidentifying voltage 14,, due to sounding information originating from aschool of fish 17, a quick transverse deflection will again produce anareal brightening 32 on the screen 22 of the cathode-ray tube 20.

The transfer of the direction 7 of the main axis 15 corresponding to thesetting of phase setter 48, to the direction of deflection of theelectron beam in the cathode-ray tube 20 need not be discussed at thispoint since a plurality of circuits are known for this purpose, e.g.,from the radar art. German Pat. No. 1,162,727 also relates to thisproblem.

In the embodiments according to FIGS. 1 and 8 the determination of themomentary frequency f was accomplished by means of a combination of aSchmitt trigger 28 with a digital-analog converter 26. It is alsounderstood however that other commercially available frequency metersoperating according to different principles can also be used for thispurpose within the scope of the present invention, so long as theyfurnish a voltage as their measuring value.

Whereas the basic circuit arranged according to the present inventionwithin the sounding system 1a of FIG. 8 still coincides with that ofFIG. 1, the embodiment shown in FIG. 9 shows a different realization ofthe circuit arrangement according to the present invention.

The sounding system lb in FIG. 9 substantially consists of a phasecoincidence correlator 53 with a subsequently connected integrationmember 54 which integrates during the observation period AT. The phasecoincidence correlator 53 acts as a phase discriminator between the tworeceived voltages 14 and M g and has one of its inputs directlyconnected to the two groups of resonators 12a and 12b of base 11 and theother of its inputs connected to the resonator via a broadband-action 90phase shifter 55. The operation of this phase coincidence correlator 53which is part of the state of the art in the communications artapplication of the correlation technique, is identical with that of alogic multiplier according to the laws of Booles logical algebra. Theinput values are the momentary polarities of the two received voltages uand a The average value of the output voltage u of this arrangement isproportional to the direction y of the acoustical center of mass of thecovered sector of the school of fish 17 or to the angular deflection(direction 7) of an individual covered object 16, but the momentaryvalue of the amplitude of this output voltage 14,, vaccilates back andforth, due to the dimensioning of the integration member 54, with thepresence of sounding information originating from a school of fish 17due to the time delay between the arrival of the echoes at the twogroups of resonators 12a and 12b and consequently producing the blurredareal brightening 32 as the indication on the screen 22 of thecathode-ray tube 20.

By pivoting base 11 or by electronically pivoting thetransmitting/receiving characteristic 14 with the aid of the phasesetter 48 or in other embodiments of radar systems by varying the centerfrequency f of the oscillations 4 and by observing the representedsounding information on the screen 22, the fisherman can then easilydetermine the expansion of the school of fish 17 without being misled byindividual reflecting objects 16 which are also reported, since thelatter are distinguished by the limited-size luminous dots 30.

According to the present invention it is therefore possible for the userto supplement the known fish locating devices with an additional deviceaccording to the present invention in a manner which is technicallysimpler and sensible to operate with respect to the representation ofthe sounding information so that the fisherman can clearly see from theprojected indication whether the sounded object is a single reflector ora congregation of individual objects, i.e., an entire school of fish.Preliminary practical tests with such a device in conjunction with amechanically pivotal base have indicated, for example, during forwardsounding, the congregation of a school of fish, and after passagethereover with the dragged net the rearward sounding indicated theirseparation into two halves which appeared on the screen of a cathode-raytube as two areal indications and the compact, since partially filled,net as a bright spot of light.

It will be understood that the above description of the presentinvention is susceptible of various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim:

1. In a sonar system, particularly for use for deep-sea fishing,including a transmitting means for the directed emission of keyed pulseseach of which comprises a plurality of non-monochromatic oscillations,and a receiving means provided with means for converting the receivedsignals into an indication of the ranging information, the improvementwherein:

a. said transmitting means includes means for providing keyed pulses ofa relatively long duration with each of said pulses having a distinctpredetermined time arrangement of its oscillations, and beingbroadbanded when compared with its characteristic center frequency; and

. said receiving means includes means responsive to the received signalsfor producing an identifying voltage proportional to the instantaneousfrequency of the received signal and means for applying said identifyingvoltage to said converting means to modulate said indication, wherebythe resulting indication represents whether the received signaloriginated from an individual object or from a bunched group of objects.

2. A sonar system as defined in claim 1 wherein said keyed pulseproviding means includes means for linearly frequency-modulating saidcenter frequency in order to provide the distinct time arrangement ofthe oscillation in each pulse.

3. A sonar system as defined in claim 1 wherein said keyed pulseproviding means includes means for shifting the phase of said centerfrequency according to a predetermined code in order to provide saiddistinct time arrangement of the oscillations in each pulse.

4. A sonar system as defined in claim 1 wherein said keyed pulseproviding means includes means for alternating said oscillations betweenat least two different frequencies according to a predetermined code inorder to provide said distinct time arrangement of the oscillations ineach pulse.

5. A sonar system as defined in claim 1 wherein said means for producingthe identifying voltage proportional to the instantaneous frequency isresponsive to the number of zero crossings of the voltages correspondingto the signals during a predetermined time period which is short whencompared with the duration of the transmitted pulses in order to producesaid identifying voltage.

6. A sonar system as defined in claim 5 wherein said predetermined timeperiod is of the order of magnitude of the period of said centerfrequency of the oscillations.

7. A sonar system as defined in claim 6 wherein said means for producingsaid identifying voltage comprises a Schmitt trigger having the receivedsignals applied to the input thereof and a digital-analog converterresponsive to the output pulses therefrom.

8. A sonar system as defined in claim 1 wherein said converting meansincludes a cathode-ray tube the beam of which is brightness controlledby the received signals and is deflected in a first direction inaccordance with the ranging information, and wherein said identifyingvoltage is applied to said tube to deflect said beam in a directiontransverse to said first direction.

9. A sonar system as defined in claim 1 wherein said converting meansincludes a recorder for the optical representation of the ranginginformation, and wherein means responsive to said identifying voltageare provided for deflecting the writing member of said recorder in adirection transverse to its distance-proportional movement.

10. A sonar system as defined in claim 1 wherein said converting meansincludes means producing an audible representation of the ranginginformation, and wherein said receiving means includes means formodulating the received signal with said produced identifying voltage.

II. A sonar system as defined in claim wherein said modulating meansfrequency modulates said received signals with said identifying voltage.

12. A sonar system as defined in claim 11 wherein said modulating meansadditionally amplitude modulates said received signals with saididentifying voltage.

13. A sonar system as defined in claim 1 wherein the pulses aretransmitted and received by means of a pair of spaced transducer meansand wherein said receiving means includes: a phase measuring meansperiodically connected to both of said transducer means and tuned toapproximately said center frequency of the transmitted oscillations fordetermining the direction of the received echoes by forming a phaseproportional voltage; a cathode-ray tube whose beam isbrightness-controlled by the received signals when an echo arrives,means for producing and applying a distance-proportional signal to thedeflection system of said cathoderay tube to deflect said beam in afirst direction, said distance deflection voltage producing means beingperiodically triggered in synchronism with the emission of thetransmitted pulses; means responsive to said phase proportional voltageand to said distance proportional voltage for producing and applying adirectional voltage signal to the deflection system of said cathoderaytube for deflecting said beam in a direction transverse to said firstdirection; and, means for modulating said directional voltage signalwith said identifying signal.

14. A sonar system as defined in claim 8 wherein the pulses aretransmitted and received by means of a pair of spaced transducer means,and wherein said means for producing said identifying voltage comprises:a phase coincidence correlator means acting as a phase discriminatorwhose output is connected to an integrating means for integrating theinput signals thereto over a period of time which is short when comparedwith the duration of the transmitted pulses, said phase coincidencecorrelator means having one of its inputs directly connected to one ofsaid pair of transducer in ans (1 the other of the inputs connected tothe ot er 0 said pair of transducer means via a broadband phase shifter.

1. In a sonar system, particularly for use for deep-sea fishing,including a transmitting means for the directed emission of keyed pulseseach of which comprises a plurality of non-monochromatic oscillations,and a receiving means provided with means for converting the receivedsignals into an indication of the ranging information, the improvementwherein: a. said transmitting means includes means for providing keyedpulses of a relatively long duration with each of said pulses having adistinct predetermined time arrangement of its oscillations, and beingbroadbanded when compared with its characteristic center frequency; andb. said receiving means includes means responsive to the receivedsignals for producing an identifying voltage proportional to theinstantaneous frequency of the received signal and means for applyingsaid identifying voltage to said converting means to modulate saidindication, whereby the resulting indication represents whether thereceived signal originated from an individual object or from a bunchedgroup of objects.
 2. A sonar system as defined in claim 1 wherein saidkeyed pulse providing means includes means for linearlyfrequency-modulating said center frequency in order to provide thedistinct time arrangement of the oscillation in each pulse.
 3. A sonarsystem as defined in claim 1 wherein said keyed pulse providing meansincludes means for shifting the phase of said center frequency accordingto a predetermined code in order to provide said distinct timearrangement of the oscillations in each pulse.
 4. A sonar system asdefined in claim 1 wherein said keyed pulse providing means includesmeans for alternating said oscillations between at least two differentfrequencies according to a predetermined code in order to provide saiddistinct time arrangement of the oscillations in each pulse.
 5. A sonarsystem as defined in claim 1 wherein said means for producing theidentifying voltage proportional to the instantaneous frequency isresponsive to the number of zero crossings of the voltages correspondingto the signals during a predetermined time period which is short whencompared with the duration of the transmitted pulses in order to producesaid identifying voltage.
 6. A sonar system as defined in claim 5wherein said predetermined time period is of the order of magnitude ofthe period of said center frequency of the oscillations.
 7. A sonarsystem as defined in claim 6 wherein said means for producing saididentifying voltage comprises a Schmitt trigger having the receivedsignals applied to the input thereof and a digital-analog converterresponsive to the output pulses therefrom.
 8. A sonar system as definedin claim 1 wherein said converting means includes a cathode-ray tube thebeam of which is brightness controlled by the received signals and isdeflected in a first direction in accordance with the ranginginformation, and wherein said identifying voltage is applied to saidtube to deflect said beam in a direction transverse to said firstdirection.
 9. A sonar system as defined in claim 1 wherein saidconverting means includes a recorder for the optical representation ofthe ranging information, and wherein means responsive to saididentifying voltage are provided for deflecting the writing member ofsaid recorder in a direction transverse to its distance-proportionalmovement.
 10. A sonar system as defined in claim 1 wherein saidconverting means includes means producing an audible representation ofthe ranging information, and wherein said receiving means includes meansfor modulating the received signal with said produced identifyingvoltage.
 11. A sonar system as defined in claim 10 wherein saidmodulating means frequency modulates said received signals with saididentifying voltage.
 12. A sonar system as defined in claim 11 whereinsaid modulating means additionally amplitude modulates said receivedsignals with said identifying voltage.
 13. A sonar system as defined inclaim 1 wherein the pulses are transmitted and received by means of apair of spaced transducer means and wherein said receiving meansincludes: a phase measuring means periodically connected to both of saidtransducer means and tuned to approximately said center frequency of thetransmitted oscillations for determining the direction of the receivedechoes by forming a phase proportional voltage; a cathode-ray tube whosebeam is brightness-controlled by the received signals when an echoarrives, means for producing and applying a distance-proportional signalto the deflection system of said cathode-ray tube to deflect said beamin a first Direction, said distance deflection voltage producing meansbeing periodically triggered in synchronism with the emission of thetransmitted pulses; means responsive to said phase proportional voltageand to said distance proportional voltage for producing and applying adirectional voltage signal to the deflection system of said cathode-raytube for deflecting said beam in a direction transverse to said firstdirection; and, means for modulating said directional voltage signalwith said identifying signal.
 14. A sonar system as defined in claim 8wherein the pulses are transmitted and received by means of a pair ofspaced transducer means, and wherein said means for producing saididentifying voltage comprises: a phase coincidence correlator meansacting as a phase discriminator whose output is connected to anintegrating means for integrating the input signals thereto over aperiod of time which is short when compared with the duration of thetransmitted pulses, said phase coincidence correlator means having oneof its inputs directly connected to one of said pair of transducer meansand the other of the inputs connected to the other of said pair oftransducer means via a broadband 90* phase shifter.